Common vernacular is commonly wrong, we get it. Yes, you can be referred to as "Doctor" with a PhD in Physics, English, or History.
Guess what? If there was an emergency on a plane and the staff called out for a Doctor, and somebody with a PhD in structural engineering stood up, you'd be yelled at.
Anyway in a pinch you can be fairly sure that any non-medical doctor is extremely (maybe narrowly) educated, whatever that's worth. A young MD might be less appropriate.